Construction of electronic systems C.Bohm Components + connections 2-pole (resistors), 3-pole...
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Transcript of Construction of electronic systems C.Bohm Components + connections 2-pole (resistors), 3-pole...
Construction of electronic systemsC.Bohm
Components + connections
2-pole (resistors), 3-pole (transistors)4-pole (transformers)+..+10-pole vacuum tubes)
First one used components mounted on isolating cards, connected by soldered connections
John Pinkerton
Increased component density demanded other methods Integrated circuits + single or double sided circuit boardsDIL (dual in line) packages wire wrapped circuit boardsHole mounted <30 legs
wrapped circuit boards printed circuit boards
crossing leads problems with single sided boards (can be solved by jumpers)
You can use vias on double sided boards (metal deposited holes usually 0.2-1 mm)
DIL
LSI (large) ic-circuits + multi layer boardsLarge DIL <100 legs many routing layersPGA (pin grid array) better <350 legs
PGA
Special power planes supply power to the components
Active component
Long connections have inductance
Varying current transport
“Ground bounce”
Power plane with low inductance
Nearby decoupling capacitorsDeliver charges that can supply the current transientsThey work like energy reservoirs
Ground plane with low inductance Ground and power plane have also good shielding properties
Low frequentSignal current
Return current
Minimizeresistance
Minimizeinductance
Return currentHigh frequentSignal current
A cut in the ground plane forces the return current to deviatewhich affects the signal quality
A cut in the ground plane can also increasethe cross talk between nearby signals
Micro strip Stripline
Wide trace and small distance gives a largecapacitance – difficult to drive
Circuit board materials:FR4 (flame retardent 4)Roger (brand name) high speedPoly imide (Kapton) – flexfoïls
Rigid flex = combination FR4-Flex foil
Multi layer boards allows blind and covered vias
Surface mounting usually < 10 layersHigher densities trace widths >0.1mm vias > 0.25mm
SO PQFP BGA≤28 legs <400 legs <600 legs
>0.5 mm/leg >0.4mm/leg 1.27mm/leg
blind
dold
Vias through power planes Via to powerplane
Drop via Thermal via to simplifysoldering
Sufficiently large diameterto matchThe drill tolerance
Usually <10 layersTrace widths>0.1 mmIsolations distance>0.1 mmVias>0.25 mm dia
blind
covered
Thruhole
micro BGA, CSP <2000 <1mm/leg
Difficult to extract the signals between the balls
Many layers are needed
Alternative: use laser drilled thin micro via layers which
supports very thin traces
Pictures from elektrotryck.se
Pictures from elektrotryck.se
Laser drilled vias
Step#1 Film Generation:
Generated from your design files, we create an exact film representation of your design. We will create one film per layer.
Step#2 Shear Raw Material:
Industry standard 0.059" thick, copper clad, two sides. Panels will be sheared to accommodate many boards.
Step#3 Drill Holes:
Using NC machines and carbide drills.
Step#4 Electroless Copper:
Apply thin copper deposit in hole barrels.
From PCBpro.com
Step#5 Apply Image:
Apply photosensitive dryfilm (plate resist) to panel. Use light source and film to expose panel. Develop selected areas from panel.
Step#6 Pattern Plate:
Electrochemical process to build copper in the holes and on the trace area. Apply tin to surface.
Step#7 Strip & Etch:
Remove dryfilm, then etch exposed copper. The tin protects the copper circuitry from being etched.
Step#8 Solder mask:
Apply solder mask area to entire board with the exception of solder pads.
From PCBpro.com
Step#9 Solder coat:
Apply solder to pads by immersing into tank of solder. Hot air knives level the solder when removed from the tank.
Step#10 Nomenclature:
Apply white letter marking using screen printing process
Step#11 Fabrication:
Route the perimeter of the board using NC equipment
From PCBpro.com
PCB manufacture · PCB laminate about 0.2mm – different types: FR4, Polyimide (Kapton) and Roger· drill· electrolytic plating of holes– connect a voltage source to the two sides while in a bath· add photo resist· illuminate pattern· rinse· etch· build the layer chemically· glue several layer· component print· lack layer· test with beds of nails or flying probes
Mounting components
Hole mounting · mount components· wave soldering· test Surface mounting · solder mask· spread solder paste· mount components (with robot)· heat in oven· next side· test
Circuit board data
generate pattern for the different layers – artwork
generate drill files
Control files to milling machine (to separate and shape the boards)
Different layers
Cupper pattern
Component print
Lack layer
Solder mask
Different physical layers (artwork order)
1 signal_1 pad_1
2 power_1
3 power_2
4 signal_2 pad_2
Start by creating a schematic
Decide board size – shape, silkscreen print, mounting holes, placing and routing zones
Make sure there is a pattern for each component – pads, holes, vias and component print
connect schematic symbols with legs to component pattern with pads
package circuit board data – translate schematics with symbols to component pattern and net list
place components on the board (side, position, orientation, ref nr) – manual, automatic or combined
draw traces in the connection layer (with support from schematics) – manual, automatic or combined –
different trace which gives different impedances
split ground plane – avoid couplings between analogue and digital parts
area fills – fill empty areas with grounded cupper surfaces
Soldering
Soldering in solder oven:
Temperature profile
Solder quality
Inferior wetting depend on poor heating or insufficient amount of flux
Lead free solder enforced in industry – higher temperatures
Conductive glue is sometimes an alternative
OK
För lite lödtenn
Dålig vätning
Not enough solder
Insufficient wetting
OK
Double sided mountingdifficult
ESD-protection ESD = Electrostatic Discharge
ESD floors (ground conductive floors)ESD shoes (ground feet against floors)ESD wrist band (grounds arm against table top)
time
Fai
lure
rat
e
Burn-in
ESD damage
At 50% humidity the human discharges rarely produce more than 2000VAt 5% they can easily reach 15000V
Inputs are often protected by diodes
Bath tub curveBurn-in
Accelerated aging at elevated temperatures
Shaking to provoke cold solder joints
Thermal cycling